Wow, this girl seems very immature. Definitely don't fuel her behavior by letting he know it gets under you skin(even in the slightest). I haven't been bullied, so I am unable to speak out of experience, but I suppose a good way to go about this is to do as others have suggested. If anything, don't get mad at her. Fighting fire with fire is a bit redundant. When she tries to get at you, just smile.

Good luck.